1. Field of the Invention
The present invention relates to power pins of a connector on a printed wiring board for receiving a removable module, and particularly relates to reducing non-uniformity in current flowing through the various power pins of such a connector.
2. Description of the Related Art
A motherboard is well understood to be a printed wiring board which includes at least one socket or connector into which a smaller printed wiring board or a packaged component is inserted. Frequently, the motherboard within an electronic system is the main circuit board and may also be the largest circuit board within the system. As is well known in the art, motherboards usually include multiple wiring layers for making interconnections between the various components attached thereto. In its simplest form, a printed wiring board need only include one wiring layer, but most motherboards usually include several wiring layers. For example, four wiring layers are commonly used, two of which are internal layers of the printed wiring board, and the other two wiring layers are formed on the outside two surfaces of the printed wiring board. In other cases, motherboards may include a number of wiring layers far greater than four, but for cost reasons, four wiring layers are frequently encountered in reasonably low cost motherboards.
One or more of these wiring layers may be arranged to provide one or more large planar conductive areas, or xe2x80x9cplanesxe2x80x9d, within the layer. Such conductive planes provide an effective way to convey power supply voltages (as well as a xe2x80x9cgroundxe2x80x9d or other reference voltage) to the leads of integrated circuits, components, and connectors attached to the printed wiring board in a manner that has both low impedance and low inductance. These conductive planes are frequently called xe2x80x9cpower planesxe2x80x9d irrespective of whether an actual xe2x80x9cpower supplyxe2x80x9d voltage, a xe2x80x9cgroundxe2x80x9d reference voltage, an analog reference voltage, or some other voltage is actually conveyed on the conductive plane. As used herein, the term xe2x80x9cpower planexe2x80x9d should not be viewed as suggesting that a xe2x80x9cpower supplyxe2x80x9d voltage need be conveyed on such a power plane. In some cases, an entire wiring layer is utilized to provide a conductive plane for a particular power supply voltage or-ground potential. In other cases, a portion of a wiring layer is used to provide a conductive plane in a region of the board. This is particularly effective when multiple voltages are routed to different sections of the motherboard.
At least one connector is usually associated with the motherboard which provides a way to attach a removable module to the motherboard. Frequently, more than one connector may be provided on a single motherboard. Examples of commonly encountered removable modules include a CPU module, a DIMM memory module, a graphics processor module, as well as other removable sub-circuits implemented as removable cards. Examples of such cards include ISA-bus cards, PCI-bus cards, and others. The magnitude of the current flowing through each of the power pins of the connector is of particular importance whenever a removable module is inserted in a connector attached to a motherboard. Most connectors, by design, limit the magnitude of current flowing through each such pin to a particular value. In some cases, modem connectors are limited to no more than one ampere (i.e., 1 A) of current per connector pin. In the case of modem CPU modules, the total current consumed by the module may easily be upwards of 30 amps. Even with a large number of pins within the connector allocated as power pins for a given power supply or ground connection to a power plane, the design of both the motherboard and the module must ensure that each such power pin conducts a current no higher than the design limit for the particular connector utilized.
While such maximum current flow limits may be problematic for many kinds of removable modules, the problems are particularly worrisome in the case of modem CPU modules, where the amount of current consumed by the module is typically so much greater than with other kinds of removable modules. Previously, most removable modules consumed much less power than is consumed by many of the modern removable modules, and the current limitations per connector pin were rarely exceeded, even when scant attention was paid to the amount of current flowing through each power pin. However, as removable modules conducting far higher currents than in the past are more widely utilized, additional care is needed to ensure that the maximum current per connector pin is not exceeded.
In spite of the long history of motherboards which accommodate removable modules, the particular problems of high current through connector power pins are relatively new, and are getting worse with each new generation of microprocessors. Consequently, there is still a need for improvements in motherboard and module design.
The aggregate current carrying capacity of a connector may be increased by reducing the difference in current flow between power pins of the connector having the highest current flow and power pins of the connector having the lowest current flow. The current flow through all the power pins may then be operated nearer to the design maximum of the particular connector used.
In a motherboard having a connector for receiving a removable module, these objectives may be achieved by incorporating one or more of the following improvements into its design. Thicker power planes within the motherboard (as well as within the module) reduce the effective resistance per square of the power plane, and help distribute the current more evenly to a greater number of power pins of the connector. The use of multiple power planes in parallel also achieves a lower effective resistance. Multiple power terminals connecting the source of regulated power supply voltage to the power plane may be used instead of just one power terminal, for both power and ground power planes. Moreover, placing a pair of power terminals symmetrically about a line perpendicular to the connector and bisecting a particular group of power pins of the connector helps distribute the current flow through the power plane to the particular group of power pins. By placing the power terminal (or terminals) at least a certain distance from the connector (e.g., at least 15 mm), a more uniform current flow through the connector is also achieved.
The power terminals connecting to the power planes may be arranged to receive a cabled connector conveying a voltage from a source external to the motherboard. In other cases the power terminals may be arranged to connect to an output terminal of an on-motherboard voltage regulator. If the power pins of the connector are generally uniformly distributed along the connector, the perpendicular bisector of the group of power pins is aligned with the perpendicular bisector of the connector, and a pair of power terminals may be symmetrically arranged about the perpendicular bisector of the connector. Alternatively, a single power terminal may be located generally on the perpendicular bisector of the connector.
In one embodiment of the current invention, an apparatus includes a printed wiring board having a plurality of wiring layers for implementing electrical interconnections including conductive planes. A connector is attached to the printed wiring board for receiving a removable module and for providing electrical interconnections between the removable module and the printed wiring board. The connector has a first plurality of power pins connected to a conductive plane of the printed wiring board for communicating a particular voltage conveyed on the conductive plane to the removable module. At least one power terminal is connected to the conductive plane of the printed wiring board at respective locations generally symmetric to a line perpendicular to the connector and bisecting the first plurality of power pins, for operably receiving the particular voltage.
A method embodiment of the present invention is suitable for use in a printed wiring board having at least one wiring layer for implementing electrical interconnections including conductive planes, and having a connector attached to the printed wiring board for receiving a removable module and for providing electrical interconnections between the removable module and the printed wiring board, the connector having a first plurality of power pins connected to a conductive plane of the printed wiring board for communicating a particular voltage conveyed on the conductive plane to the removable module, the printed wiring board further having at least one power terminal connected to the conductive plane of the printed wiring board for operably receiving the particular voltage. A method for reducing the difference in current flow between power pins of the connector having the highest current flow and power pins of the connector having the lowest current flow includes locating the at least one power terminal at respective locations on the printed wiring board generally symmetric to a line perpendicular to the connector and bisecting the first plurality of power pins.
The present invention may be better understood, and its numerous features and advantages made even more apparent to those skilled in the art by referencing the detailed description and accompanying drawings of the embodiments described below. These and other embodiments of the present invention are defined by the claims appended hereto.